1. Field of the Invention
The present invention relates to a picture display apparatus comprising a video signal source having its video signal information components displayed by said apparatus, a horizontal scanning circuit with a line deflection coil, and a vertical scanning circuit, for displaying said picture by means of a spot on the screen of a picture tube, a beam scan velocity modulation circuit coupled to said video signal source for modulating the horizontal velocity of the spot as a function of the video content of said video signal with the aid of an auxiliary line deflection coil, and comprising a video signal differentiator circuit followed by a transconductance amplifier (i.e. an amplifier having a voltage input and a current output) having at its output a power stage of the current generator type whose current output is connected to a first terminal of the auxiliary line deflection coil. The beam scan velocity modulation circuit has for its object to achieve a neater appearance of the luminance transitions in a picture.
2. Description of the Related Art
A beam scan velocity modulation circuit is disclosed in U.S. Pat. No. 5,072,300. This document describes in detail (FIG. 3) a circuit which includes a differentiator circuit of the video signal, followed by a transconductance amplifier whose current output is connected to a first terminal of an auxiliary line deflection coil. The AC current in this coil, outputted by the second terminal, is drained towards a voltage reference terminal (ground) across a coupling capacitor. A problem encountered in assemblies of this type is the following: in order to correct rapid luminance variations, it must be possible to produce rapid current variations in the auxiliary coil already mentioned, and as is commonly known, to accomplish this, the voltage induced by the self-induction of the coil must be overcome, which requires high supply voltages. The supply voltage utilized by the assembly of this document is 135 volts, using a coil whose self-induction has a value of 6.7 .mu.H.